On-Sun Tracking Evaluation of a Small-Scale Tensile Ganged Heliostat Prototype

Various ganged heliostat concepts have been proposed in the past. The attractive aspect of ganged heliostat concepts is multiple heliostats are grouped so that pedestals, tracking drives, and other components can be shared, thus reducing the number of components. The reduction in the number of components is thought to significantly reduce cost. However, since the drives and tracking mechanisms are shared, accurate on-sun tracking of grouped heliostats becomes challenging because the angular degrees-of-freedom are now limited for the multiple number of combined heliostats. In this paper, the preliminary evaluation of the on-sun tracking of a novel tensile-based cable suspended ganged heliostat concept is provided. In this concept, multiple heliostats are attached to two guide cables. The cables are attached to rotation spreader arms which are anchored to end posts on two ends. The guide cables form a catenary which makes tracking on-sun interesting and challenging. Tracking is performed by rotating the end plates that the two cables are attached to and rotating the individual heliostats in one axis. An additional degree-of-freedom can be added by differentially tensioning the two cables, but this may be challenging to do in practice. Manual on-sun tracking was demonstrated on small-scale prototypes. The rotation arms were coarsely controlled with linear actuators, and the individual heliostats were hand-adjusted in local pitch angle and locked in place with set screws. The coarse angle adjustments showed the tracking accuracy was 3–4 milli-radians. However, with better angle control mechanisms the tracking accuracy can be drastically improved. In this paper, we provide tracking data that was collected for a day, which showed feasibility for automated on-sun tracking. The next steps are to implement better angle control mechanisms and develop tracking algorithms so that the ganged heliostats can automatically track.

Optical Ray-Tracing Performance Modeling of Quartz Half-Shell Tubes Aperture Cover for Falling Particle Receiver

A 1 MWt falling particle receiver prototype was designed, built and is being evaluated at Sandia National Laboratories, National Solar Thermal Test Facility (NSTTF). The current prototype has a 1 m2 aperture facing the north field. The current aperture configuration is susceptible to heat and particle losses through the receiver aperture. Several options are being considered for the next design iteration to reduce the risk of heat and particle losses, in addition to improving the receiver efficiency to target levels of ∼90%. One option is to cover the receiver aperture with a highly durable and transmissive material such as quartz glass. Quartz glass has high transmittance for wavelengths less than 2.5 microns and low transmittance for wavelengths greater than 2.5 microns to help trap the heat inside the receiver. To evaluate the receiver optical performance, ray-tracing models were set up for several different aperture cover configurations. The falling particle receiver is modeled as a box with a 1 m2 aperture on the north side wall. The box dimensions are 1.57 m wide × 1.77 m tall × 1.67 m deep. The walls are composed of RSLE material modeled as Lambertian surfaces with reflectance of either 0.9 for the pristine condition or 0.5 for soiled walls. The quartz half-shell tubes are 1.46 m long with 105 mm and 110 mm inner and outer diameters, respectively. The half-shell tubes are arranged vertically and slant forward at the top by 30 degrees. Four configurations were considered: concave side of the half-shells facing away from the receiver aperture with (1) no spacing and (2) high spacing between the tubes, and concave side of the half-shells facing the aperture with (3) no spacing and (4) high spacing between the tubes. The particle curtain, in the first modeling approach, is modeled as a diffuse surface with transmittance, reflectance, and absorptance values, which are based on estimates from previous experiments for varying particle flow rates. The incident radiation is from the full NSTTF heliostat field with a single aimpoint at the center of the receiver aperture. The direct incident rays and reflected and scattered rays off the internal receiver surfaces are recorded on the internal walls and particle curtain surfaces as net incident irradiance. The net incident irradiances on the internal walls and particle curtain for the different aperture cover configuration are compared to the baseline configuration. In all cases, just from optical performance alone, the net incident irradiance is reduced from the baseline. However, it is expected that the quartz half-shells will reduce the convective and thermal radiation losses through the aperture. These ray-tracing results will be used as boundary conditions in computational fluid dynamics (CFD) analyses to determine the net receiver efficiency and optimal configuration for the quartz half-shells that minimize heat losses and maximize thermal efficiency.

Evaluating the Energy Savings From Community Scale Solar Water Heating in Los Angeles County: Residential Case Studies

Estimation of Energy Savings from Community Scale Solar Water Heating in Los Angeles County explores the extent to which community scale solar water heating systems, designed for residential structures in Los Angeles County and constructed from currently available technology, can displace natural gas for domestic water heating through a series of case studies. The effects of policy, urban form, and building characteristics on the performance of solar water heating systems, as well as community scale solar water heating’s potential to reduce emissions from the residential housing sector, are discussed herein. Three public and three private residential developments were selected as case studies for community scale solar water heating, with numbers of units and residents ranging from the tens to hundreds. These six cases were draw from the pool of approximately 19,000 “energy communities” in Los Angeles County, i.e. residential developments where the installation and operation of community scale solar water heating systems is broadly feasible. The six properties were also chosen to represent a cross-section housing stock and development patterns common in Los Angeles County, and different levels of suitability for solar water heating. The performance of and energy savings from solar water heating systems on each of these properties is then evaluated using the National Renewable Energy Laboratory’s System Advisor Model (NREL SAM). The results of the system simulations reveal how building characteristics and hot water demand affect the performance of community scale solar water heating systems. The case study sites’ system simulations show that residential developments with community scale solar water heating systems reach an average solar fraction of 50%. The results of the case studies indicate that community scale solar water heating is viable as an emissions reduction technology for the residential building sector in Mediterranean climates. However, side-by-side comparison with solar PV systems and other water heating technologies (such as grid-connected heat pumps) is necessary to determine optimality in terms of cost, emissions reduction, and thermal efficiency) in specific contexts.

A System Analysis of Pressurized Electrolysis for Compressed Hydrogen Production

Renewable production of hydrogen offers a clean and sustainable replacement of fossil fuels. As an energy carrier hydrogen is compressed and stored at high pressures. Pressurized water electrolysis improves plant performance as hydrogen compression is an energy intensive process. This work analyzes hydrogen production over the temperature range of 100°C to 800°C and pressure range of 1 bar to 700 bar. The sensitivity of plant efficiency to hydrogen compression technology and waste heat recovery is investigated. This study reveals that a lower-heating-value electric energy efficiency of 84% can be achieved when pressurized electrolysis avoids the inefficiencies of hydrogen compression. With the availability of high-quality waste heat plant efficiency can reach 98% for a pipeline distribution scenario at 3MPa. When no waste heat is available plant efficiency is independent of electrolysis temperature. For hydrogen use in the transportation sector, pressurized supercritical water electrolysis at 800°C has the potential to improve plant efficiency by 14% from a baseline of non-pressurized electrolysis at 800°C.

Building Stock Inertia and Impacts on Energy Consumption and CO2 Emissions in Qatar

Greenhouse gas emission reduction and the consequent decrease in the environmental impacts of fossil fuel can be achieved by cutting back on energy consumption in the building sector that consumes around 30% of total final energy around the globe. The building sector is a complex component of the modern economy and life and includes diverse types of structures, uses, and energy patterns. Such variability is a result of the way that buildings are designed, built, and used in addition to the variations of their materials, equipment, and users. From the start of the construction phase until their demolition, buildings involve energy consumption. A single building’s energy consumption pattern can be called its energy inertia, that is the way it consumes energy throughout its lifetime. Energy consumption also varies according to the age of the buildings. As a building gets older, its structure and equipment start losing their efficiency and often lead to increasing energy consumption over time. At any given time, the building sector is composed of structures of various ages. Some are under construction, others are recently built, some have lived to be mature and some quite old enough to be demolished. This complexity in the building sector creates a momentum against implementation of policies that reduce energy consumption. In this study, a system dynamic model is developed to perceive the temporal evolution of energy consumption and efficiency measures for the villa-type building stock in Qatar. This model tests energy efficiency policy measures such as renovation rates of 15 and 30 years, for buildings that are considered old, and also examines implementation of technology and building codes for new buildings. Results reveal savings of between 157 GWh and 1,275 GWh of electricity and reduction in CO2 emissions ranging from 77,000 tonnes to 602,000 tonnes.

Thermodynamic and Performance Study of Solar Regenerative Organic Rankine Cycle System for Use in Residential Micro-Combined Heat and Power Generation

A continued increase in both energy demand and greenhouse gas emissions (GHGs) call for utilising energy sources effectively. In comparison with traditional energy set-ups, micro-combined heat and power (micro-CHP) generation is viewed as an effective alternative; the aforementioned system’s definite electrical and thermal generation may be attributed to an augmented energy efficiency, decreased capacity as well as GHGs percentage. In this regard, organic Rankine cycle (ORC) has gained increasing recognition as a system, which is capable for generating electrical power from solar-based, waste heat, or thermal energy sources of a lower quality, for instance, below 120 °C. This study focuses on investigating a solar-based micro-CHP system’s performance for use in residential buildings through utilising a regenerative ORC. The analysis will focus on modelling and simulation as well as optimisation of operating condition of several working fluids (WFs) in ORC in order to use a heat source with low-temperature derived from solar thermal collectors for both heat and power generation. A parametric study has been carried out in detail for analysing the effects of different WFs at varying temperatures and flowrates from hot and cold sources on system performance. Significant changes were revealed in the study’s outcomes regarding performance including efficiency as well as power obtained from the expander and generator, taking into account the different temperatures of hot and cold sources for each WF. Work extraction carried out by the expander and electrical power had a range suitable for residential building applications; this range was 0.5–5 kWe with up to 60% electrical isentropic efficiency and up to 8% cycle efficiency for 50–120 °C temperature from a hot source. The operation of WFs will occur in the hot source temperature range, allowing the usage of either solar flat plate or evacuated tube collectors.

Experimental Study on Performance of a Single-Cylinder Engine Fuelled With Diesel and Vegetable Oil-Diesel Blends

Continuous demand for energy in order to provide to an ever-increasing global population calls for use of or integration of other alternative sources of fuel other than fossil fuels. Many countries all over the world use vegetable oils blended with neat diesel as alternative and using these biofuels can help alleviate lessen the emissions releases on the environment as well as the country’s dependency on fossil fuels. In the Philippines Coconut Methyl Ester (CME) is the primary vegetable oil used, however in this study we used four other vegetable oils which are RCO (Refined Corn Oil), RPO (Refine Palm Oil), JFO (Jahtropa Filtered Oil) and JME (Jathropa Methyl Ester) in order to investigate the possibility of their use in diesel engines. A 6.3 kW single-cylinder, four stroke cycle, direct injection engine was used for the study. This kind of engine is typically used in the Philippines for different purposes such as backup power for households, for boats, pumps and for agriculture use. The specific fuel consumption of the biodiesel blends compared to neat diesel fuel ranged from −15% to 15% with RCO and JME having higher SFC and JFO and RPO having lower SFC. Fuel conversion efficiency of the varied from −12% to 12% with JFO and RPO having higher efficiency and RCO and JME having lower efficiency. The power of the varied from −7% to 6% with RPO having lower power output, JFO having higher power output and JME and RCO having similar power output to neat diesel fuel. At full load condasition Neat Diesel Fuel blended with 15% Refined Palm Oil showed the greatest improvement in SFC while Neat Diesel Fuel blended with 10% Jathropa Filtered Oil showed the best power output.

Parametric Analysis of Particle CSP System Performance and Cost to Intrinsic Particle Properties and Operating Conditions

The use of solid particles as a heat-transfer fluid and thermal storage media for concentrating solar power is a promising candidate for meeting levelized cost of electricity (LCOE) targets for next-generation CSP concepts. Meeting these cost targets for a given system concept will require optimization of the particle heat-transfer fluid with simultaneous consideration of all system components and operating conditions. This paper explores the trade-offs in system operating conditions and particle thermophysical properties on the levelized cost of electricity through parametric analysis. A steady-state modeling methodology for design point simulations dispatched against typical meteorological year (TMY) data is presented, which includes computationally efficient submodels of a falling particle receiver, moving packed-bed heat exchanger, storage bin, particle lift, and recompression supercritical CO2 (sCO2) cycle. The components selected for the baseline system configuration presents the most near-term realization of a particle-based CSP system that has been developed to date. However, the methodology could be extended to consider alternative particle receiver and heat exchanger concepts. The detailed system-level model coupled to component cost models is capable of propagating component design and performance information directly into the plant performance and economics. The system-level model is used to investigate how the levelized cost of electricity varies with changes in particle absorptivity, hot storage bin temperature, heat exchanger approach temperature, and sCO2 cycle operating parameters. Trade-offs in system capital cost and solar-to-electric efficiency due to changes in the size of the heliostat field, storage bins, primary heat exchanger, and receiver efficiency are observed. Optimal system operating conditions are reported, which approach levelized costs of electricity of $0.06 kWe−1hr−1.

Numerical Simulation of a Composite Metal Foam-PCM Air Heat Exchanger Using Rod PTC Heating Elements

The aim of this paper is to study the charging/discharging process in a Latent heat exchanger for the purpose of space heating by using a composite metal foam/PCM. The composite PCM-air system is modelled in a 3-D CFD approach for the purpose of 8h charging during the night and 16h discharging during the daytime using the non-equilibrium thermal model to simulate the presence of a porous medium in the domain. For the charging process, rod Positive Temperature Coefficient (PTC) heating elements with constant temperature are selected to heat the PCM based on the maximum operating temperature of the PCM. For the discharging process, a blower is assumed to pass the air from the middle of the PCM container and so the air can gain heat and its temperature rises which is used then for space heating. RT70HC is also selected as the PCM material due to the high capacity of latent heat and suitable melting point for domestic usage. The system is studied according to the average liquid fraction and temperature of the PCM during both charging and discharging as well as the outlet temperature of the air during discharging. The results show that by using two rod heating elements with the diameter of 1cm, length of 25cm and temperature of 95°C, the melting process is performed in less than 8h. Furthermore, a uniform output temperature of almost 29.5°C is also achieved in the next 16h during the discharging process with the air mass flow rate of 0.04 kg/s.

Sustainable Biodiesel Production From Blends of Waste Cooking Oil and Microalgae Oil

Waste cooking oil and microalgae oil could become alternative raw materials for biodiesel production in the global quest for energetic sustainability. However, the technical and economic viability of the biodiesel production process from these alternative sources has not been fully investigated yet, within the knowledge of the authors. Therefore, the main objective of this study is to carry out an exergetic and economical analysis of the biodiesel production process from blends of waste cooking oil and microalgae oil. Initially, the mass, energy and exergy balances of the process of the biodiesel production was conducted. Then, an optimization procedure was executed with the selected objective functions. The results showed that it is possible to optimize the process as a function of the ratio of destroyed exergy system by the amount of ester produced, generating a profit of $ 29.50 per second, for an ratio of oil/ethanol of 3.7/1. In conclusion, the proposed model can also be used in the future for performing the exergoeconomic optimization of biodiesel production processes from blends of waste cooking oil and microalgae oil, aiming at achieving process sustainability.